The present invention relates to capability negotiation in a telecommunications network and in particular, though not necessarily, to the negotiation of a suitable speech codec.
Telecommunications networks currently rely to a large extent upon the Signalling System no.7 (SS7) as the mechanism for controlling call connections and for handling the transfer of signalling information between signalling points of the networks.
Typically, one or more application and user parts at a given signalling point will make use of SS7 to communicate with peer application and user parts at some other signalling point. Examples of user parts are ISUP (ISDN User Part) and TUP (Telephony User Part) whilst examples of application parts are INAP (Intelligent Network Application Part) and MAP (Mobile Application Part). The conventional SS7 protocol stack includes Message Transfer Parts MTP1, MTP2, and MTP3 which handle the formatting of signalling messages for transport over the physical layer as well as various routing functions.
There has been considerable interest of late amongst the telecommunications community in using non-standard (i.e. non-conventional within the telecommunications industry) signalling transport mechanisms in telecommunications networks in place of the conventional SS7 mechanisms. The reasons for this are related both to improvements in efficiency as well as potential cost savings. Much consideration has been given for example to the use of Internet Protocol (IP) networks to transport signalling information between signalling points. IP networks have the advantage that they make efficient use of transmission resources by using packet switching and are relatively low in cost due to the widespread use of the technology (as opposed to specialised telecommunication technology). There is also interest in using other transport mechanisms including AAL1/2/5, FR etc.
The ISUP standard which deals with the setting-up and control of call connections in a telecommunications network is closely linked to the SS7 signalling transport mechanism and does not readily lend itself to use with other non-standard transport technologies such as IP and AAL2. As such, several standardisation bodies including the ITU-T, ETSI, and ANSI, are currently considering the specification of a signalling protocol for the control of calls, which is independent of the underlying transport mechanism. This can be viewed as separating out from the protocol, Bearer Control functions which relate merely to establishing the parameters (including the start and end points) of the xe2x80x9cpipexe2x80x9d via which user plane data is transported between nodes, and which are specific to the transport mechanism. The new protocol, referred to as Transport Independent Call Control (TICC), retains Call Control functions such as the services invoked for a call between given calling and called parties (e.g. call forwarding), and the overall routing of user plane data.
The new network architecture resulting from the separation of the call and Bearer Control levels results in an open interface appearing between a Call Control entity and a Bearer Control entity, where these entities are referred to as a Media Gateway Controller and a Media Gateway respectively. The open interface is referred to hereinafter as X-CP, examples of which are the MEGACO work of the IETF and the H.248 work of ITU Study Group 16 (SG16).
Traditionally, fixed telephone networks make use of Pulse Code Modulation to transport user plane data, e.g. voice, facsimile, etc, between network nodes. Modem cellular networks on the other hand often use one or more coders/decoders (referred to as xe2x80x9ccodecsxe2x80x9d) to compress voice signals for efficient transmission across the air interface and within the cellular networks themselves. Where a telephone call connection extends between two networks (or terminals) which support different or multiple speech codecs, a negotiation may be carried out between the terminals to decide upon an appropriate codec. If this negotiation is not carried out, the result may be a requirement for transcoding at the interface between the networks, i.e. conversion from one form of speech coding to another. Transcoding is expensive in terms of resources, significantly degrades speech quality, and introduces a processing time delay. Codec negotiation is therefore the preferred option.
In addition to codec negotiation, there is often a need in conventional telecommunications networks to negotiate other functionality and parameters. For example, it may be desirable to negotiate security capabilities such as voice ciphering and data encryption between terminals or nodes in telecommunications networks.
According to a first aspect of the present invention there is provided a method of negotiating a call capability between signalling points in a telecommunications system, the method comprising:
sending a capability preference or prioritised list of preferences from an originating signalling point to a terminating signalling point or signalling transfer point, at the Call Control level; and
returning a capability acceptance from the terminating signalling point or signalling transfer point to the originating signalling point at the Call Control level, if the terminating signalling point or signalling transfer point accepts a preference sent by the originating signalling point.
It will be appreciated that in some cases, e.g. where the terminating signalling point or signalling transfer point does not accept a capability preference (or one of a list of preferences) sent by the originating signalling point, no acceptance message may be returned in which case a default capability is assumed by both points. Alternatively, a default message may be returned indicating that the default codec is to be used. If no codec can be agreed upon, then in certain situations a call may be released due to network incompatibility.
The present invention is particularly suited to negotiating speech codec capabilities between signalling transfer points located in different telecommunications networks. For example, in Japanese telecommunications networks, the invention may be used to negotiate the use of one of VSELP, PSI-CELP, or xcexc-law coding, where claw coding is the default coding. However, the invention is also applicable to negotiating other capabilities including security capabilities (e.g. voice ciphering and data encryption).
The protocol used to conduct the negotiation may be TICC, or may be a specific protocol also employed at the CC level, i.e. a User Plane Capability Negotiation protocol.
Where the Call Control and Bearer Control levels are controlled by separate protocols, a signalling point reacts to the selection of a capability at the Call Control level by notifying the Bearer Control level, if the selection affects the bearer level. If appropriate, notifications may be subsequently sent at the bearer level between bearer switching points to enable the establishment of appropriate bearer level resources.
Preferably, the signalling point or signalling transfer point is a Media Gateway Controller. More preferably, the Media Gateway Controller communicates with one or more Media Gateways which exist at the Bearer Control level.
Despite the fact that certain options supported for a capability at the Bearer Control level may be known at the Call Control level, the Call Control level will not necessarily know the current availability of those options at the Bearer Control level. Preferably therefore, upon receipt of a capability preference or prioritised list of preferences at a terminating signalling point or signalling transfer point, the Call Control level conducts a negotiation with the Bearer Control level to determine option availability at the Bearer Control level. More preferably, this negotiation occurs between a Media Gateway Controller of the Call Control level and a Media Gateway of the Bearer Control level.
Where a prioritised list of preferences is sent from an originating signalling point to a Media Gateway Controller, the Controller preferably modifies the list to remove preferences which it knows are not supported by the associated Media Gateway. The Controller then sends the modified list to the Media Gateway which selects the preference with the highest priority which the Media Gateway can support at that time. The Gateway may then reserve the resources necessary for that preference and advises the Media Gateway Controller of the preference. The Media Gateway Controller may then return a capability acceptance to the originating Media Gateway Controller.
According to a second aspect of the present invention there is provided a signalling point arranged to negotiate a call capability with another signalling point in a telecommunications system, the method comprising:
means for sending a capability preference or prioritised list of preferences to a terminating signalling point or signalling transfer point, at the Call Control level; and
means for receiving a capability acceptance from the terminating signalling point or signalling transfer point at the Call Control level, which capability acceptance is sent if the terminating signalling point or signalling transfer point accepts a preference sent by the originating signalling point.
According to a third aspect of the present invention there is provided a Media Gateway Controller of a telecommunications system, the Media Gateway Controller comprising:
means for receiving a capability preference or prioritised list of preferences from a peer Media Gateway Controller, where said capability preference or prioritised list of preferences relate to a connection to be set-up over the telecommunications system;
means for communicating with a Media Gateway associated with the Media Gateway Controller to determine the availability of the received preference(s) at the Media Gateway; and
means for returning a capability preference acceptance message to said peer Media Gateway Controller in dependence upon the determined availability at the Media Gateway.
According to a fourth aspect of the present invention there is provided a Media Gateway of a telecommunications system, the Gateway comprising:
means for receiving a capability preference or prioritised list of preferences from a Media Gateway Controller, wherein said capability preference or prioritised list of preferences relate to a connection to be set-up over the telecommunications system;
means for selecting a preference on the basis -of the availability of the preferences at the Media Gateway; and
means for sending the selected preference to said Media Gateway Controller.
According to a fifth aspect of the invention there is provided a method of negotiating protocol options between first, second and third nodes in a telecommunications network using separated call control and bearer control protocols, the method comprising:
transmitting a first call control message from the first node to the second node specifying protocol options supported by the first node;
transmitting a second call control message from the second node to the third node specifying protocol options supported by both the first and second nodes; and
selecting a protocol option from the protocol options specified in the second control message.
Said step of selecting a protocol option from the protocol options specified in the second control message may be carried out by the third node.
Each said call control message may include a preference level associated with each specified protocol option.
The first node may be an originating node. The third node may be a terminating node.
The method may further include a step of determining whether the bearer level between the first and second nodes is affected by said selecting step, and if the bearer level is affected taking action to modify the parameters of the bearer level between the first and second nodes.
The method may also include determining whether the bearer level between the second and third nodes is affected by said selecting step, and if the bearer level is affected taking action to modify the parameters of the bearer level between the second and third nodes.
According to a sixth aspect of the present invention there is provided a method of setting-up a speech call connection in a telecommunications system where the Call Control protocol is independent of the bearer transport mechanism, the method comprising:
negotiating a first speech codec between an originating signalling point of the system and a first terminating signalling point;
establishing a call connection over the transport mechanism between the originating signalling point and said first terminating signalling point in dependence upon said first speech codec;
subsequently negotiating a second, different speech codec between said first terminating signalling point and a second, new terminating signalling point;
notifying the originating signalling point of the second speech codec; and
establishing a call connection between the originating signalling point and said second terminating signalling point wherein said first originating signalling point acts as an intermediate signalling point and wherein the first mentioned call connection is modified if necessary to support said second speech codec.
It will be appreciated that embodiments of the present invention enable the smooth transfer of a call connection between different terminating signalling points, by modifying the connection between the originating signalling point and the original terminating signalling point to reflect the new codec. The final end-to-end connection is completed by establishing a connection between the original terminating signalling point and the new terminating signalling point based upon the new codec. Preferably, this latter connection is established after the first connection is modified, although this need not be the case.
It will also be appreciated that the method of the present invention is only applicable when the speech codec-negotiation between the original terminating signalling point and the final terminating signalling point does not result in the first speech codec. If the result is the first speech codec, then there may be no need to modify the original connection.
Preferably, the step of notifying the originating signalling point of the second speech codec comprises sending an appropriate Call Control (CC) message from the original terminating signalling point to the originating signalling point. This CC message may be a Modify request message.
Preferably, the Call Control protocol is a Transport Independent Call Control (TICC) protocol.
The present invention is applicable to the evolution of existing telecommunication network such as mobile networks based on GSM, DAMPS, PDC, etc, as well as to future generation networks such as UMTS.
According to a seventh aspect of the present invention there is provided a telecommunications system in which the Call Control protocol is independent of the bearer transport mechanism, the system comprising:
means for negotiating a first speech codec between an originating signalling point of the system and a first terminating signalling point;
means for establishing a call connection over the transport mechanism between the originating signalling point and said first terminating signalling point in dependence upon said first speech codec;
means for subsequently negotiating a second, different speech codec between said first terminating signalling point and a second, new terminating signalling point;
means for notifying the originating signalling point of the second speech codec; and
means for establishing a call connection between the originating signalling point and said second terminating signalling point wherein said first originating signalling point acts as an intermediate signalling point and wherein the first mentioned call connection is modified if necessary to support said second speech codec.
According to an eighth aspect of the present invention there is provided a signalling point of a telecommunications network in which the Call Control protocol is independent of the bearer transport mechanism, the signalling point comprising:
processing means for negotiating a first speech codec with a first terminating signalling point;
means for establishing a call connection over the transport mechanism between the originating signalling point and said first terminating signalling point in dependence upon said first speech codec;
means for receiving a notification of a second speech codec which has been negotiated between said first terminating signalling point and a second, new terminating signalling point; and
means for modifying the first mentioned call connection if necessary to support said second speech codec.
According to a ninth aspect of the present invention there is provided a method of setting up a call connection between first and second mobile telephone networks at least one of which comprises a Tandem Free Operation (TFO) device located outside of the Radio Access Network part(s) of the mobile network and in which the Call Control protocol is independent of the bearer transport mechanism, the method comprising the steps of:
conducting a negotiation between said TFO device of one of the mobile networks and a peer TFO device of the other mobile network to determine a suitable speech codec; and
notifying said Radio Access Network of the determined speech codec by sending a Call Control (CC) message from the associated TFO device.
It may be the case that each of the mobile networks comprises a Tandem Free Operation (TFO) device located outside of the Radio Access network part(s) of the mobile network. However, this need not be the case, and one of the mobile networks may have a TFO device within the radio Access Network.
The two mobile telephone networks may be coupled to one another via a PSTN. Preferably, said negotiation is carried out using the Codec Mismatch Resolution and Optimisation Procedure in the TFO protocol, with TFO messages being sent using inband signalling.
Preferably, said the or each TFO device located outside of a Radio Access network is located at a Gateway MSC (GMSC) which provides an interface between the mobile network and foreign networks, e.g. a PSTN.
The present invention is particularly suited to setting up a call connection between subscribers, one of whom is a subscriber of a Universal Mobile Telecommunication System (UMTS) network. In this case, the Radio Access Network is preferably a UMTS Terrestrial Radio Access Network (UTRAN), with the TFO device of the network being located on the edge of the UMTS core network.
According to an tenth aspect of the present invention there is provided apparatus for setting up a call connection between first and second mobile telephone networks at least one of which comprises a Tandem Free Operation (TFO) device located outside of the Radio Access Network part(s) of the mobile network and in which the Call Control protocol is independent of the bearer transport mechanism, the apparatus comprising:
means for conducting a negotiation between said TFO device of one of the mobile networks and a peer TFO device of the other mobile network to determine a suitable speech codec; and
means for notifying said Radio Access Network of the determined speech codec by sending a Call Control (CC) message from the associated TFO device.
According to a eleventh aspect of the present invention there is provided a method of setting up a call connection between first and second mobile telephone networks each of which comprises a Tandem Free Operation (TFO) device located outside of the Radio Access Network part(s) of the mobile network and in which the Call Control protocol is independent of the bearer transport mechanism, the mobile networks being coupled via a Public Switched Telephone Network (PSTN), the method comprising the step of:
conducting a negotiation between two mobile terminals subscribing to the first and second mobile networks respectively to determine a suitable speech codec, wherein the negotiation is conducted using Call Control protocol signalling messages exchanged between the Radio Access Network parts and the respective TFO devices, and ISUP messages sent between the TFO devices.
For example, a list of codecs which are available to an originating mobile network may be sent from the TFO device of that network to the peer TFO device using an ISUP Initial Address Message (IAM). The message may additionally include the codec preferred by the originating mobile network. A subsequent ISUP message sent in the backward direction will indicate the codec type selected by the terminating mobile terminal. In order to enable this negotiation procedure, it may be necessary to modify the ISUP standard.
According to a twelfth aspect of the present invention there is provided apparatus for setting up a call connection between first and second mobile telephone networks each of which comprises a Tandem Free Operation (TFO) device located outside of the Radio Access Network part(s) of the mobile network and in which the Call Control protocol is independent of the bearer transport mechanism, the mobile networks being coupled via a Public Switched Telephone Network (PSTN), the apparatus comprising:
means for conducting a negotiation between two mobile terminals subscribing to the first and second mobile networks respectively to determine a suitable speech codec, wherein the negotiation is conducted using Call Control protocol signalling messages exchanged between the Radio Access Network parts and the respective TFO devices, and ISUP messages sent between the TFO devices.